_ Git - rust-lightning/blob - lightning/src/routing/utxo.rs

   1 // This file is Copyright its original authors, visible in version control
   2 // history.
   3 //
   4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
   5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
   7 // You may not use this file except in accordance with one or both of these
   8 // licenses.
   9
  10 //! This module contains traits for LDK to access UTXOs to check gossip data is correct.
  11 //!
  12 //! When lightning nodes gossip channel information, they resist DoS attacks by checking that each
  13 //! channel matches a UTXO on-chain, requiring at least some marginal on-chain transacting in
  14 //! order to announce a channel. This module handles that checking.
  15
  16 use bitcoin::{BlockHash, TxOut};
  17 use bitcoin::hashes::hex::ToHex;
  18
  19 use crate::ln::chan_utils::make_funding_redeemscript_from_slices;
  20 use crate::ln::msgs::{self, LightningError, ErrorAction};
  21 use crate::routing::gossip::{NetworkGraph, NodeId, P2PGossipSync};
  22 use crate::util::events::MessageSendEvent;
  23 use crate::util::logger::{Level, Logger};
  24 use crate::util::ser::Writeable;
  25
  26 use crate::prelude::*;
  27
  28 use alloc::sync::{Arc, Weak};
  29 use crate::sync::Mutex;
  30 use core::ops::Deref;
  31
  32 /// An error when accessing the chain via [`UtxoLookup`].
  33 #[derive(Clone, Debug)]
  34 pub enum UtxoLookupError {
  35         /// The requested chain is unknown.
  36         UnknownChain,
  37
  38         /// The requested transaction doesn't exist or hasn't confirmed.
  39         UnknownTx,
  40 }
  41
  42 /// The result of a [`UtxoLookup::get_utxo`] call. A call may resolve either synchronously,
  43 /// returning the `Sync` variant, or asynchronously, returning an [`UtxoFuture`] in the `Async`
  44 /// variant.
  45 pub enum UtxoResult {
  46         /// A result which was resolved synchronously. It either includes a [`TxOut`] for the output
  47         /// requested or a [`UtxoLookupError`].
  48         Sync(Result<TxOut, UtxoLookupError>),
  49         /// A result which will be resolved asynchronously. It includes a [`UtxoFuture`], a `clone` of
  50         /// which you must keep locally and call [`UtxoFuture::resolve`] on once the lookup completes.
  51         ///
  52         /// Note that in order to avoid runaway memory usage, the number of parallel checks is limited,
  53         /// but only fairly loosely. Because a pending checks block all message processing, leaving
  54         /// checks pending for an extended time may cause DoS of other functions. It is recommended you
  55         /// keep a tight timeout on lookups, on the order of a few seconds.
  56         Async(UtxoFuture),
  57 }
  58
  59 /// The `UtxoLookup` trait defines behavior for accessing on-chain UTXOs.
  60 pub trait UtxoLookup {
  61         /// Returns the transaction output of a funding transaction encoded by [`short_channel_id`].
  62         /// Returns an error if `genesis_hash` is for a different chain or if such a transaction output
  63         /// is unknown.
  64         ///
  65         /// [`short_channel_id`]: https://github.com/lightning/bolts/blob/master/07-routing-gossip.md#definition-of-short_channel_id
  66         fn get_utxo(&self, genesis_hash: &BlockHash, short_channel_id: u64) -> UtxoResult;
  67 }
  68
  69 enum ChannelAnnouncement {
  70         Full(msgs::ChannelAnnouncement),
  71         Unsigned(msgs::UnsignedChannelAnnouncement),
  72 }
  73 impl ChannelAnnouncement {
  74         fn node_id_1(&self) -> &NodeId {
  75                 match self {
  76                         ChannelAnnouncement::Full(msg) => &msg.contents.node_id_1,
  77                         ChannelAnnouncement::Unsigned(msg) => &msg.node_id_1,
  78                 }
  79         }
  80 }
  81
  82 enum NodeAnnouncement {
  83         Full(msgs::NodeAnnouncement),
  84         Unsigned(msgs::UnsignedNodeAnnouncement),
  85 }
  86 impl NodeAnnouncement {
  87         fn timestamp(&self) -> u32 {
  88                 match self {
  89                         NodeAnnouncement::Full(msg) => msg.contents.timestamp,
  90                         NodeAnnouncement::Unsigned(msg) => msg.timestamp,
  91                 }
  92         }
  93 }
  94
  95 enum ChannelUpdate {
  96         Full(msgs::ChannelUpdate),
  97         Unsigned(msgs::UnsignedChannelUpdate),
  98 }
  99 impl ChannelUpdate {
 100         fn timestamp(&self) -> u32 {
 101                 match self {
 102                         ChannelUpdate::Full(msg) => msg.contents.timestamp,
 103                         ChannelUpdate::Unsigned(msg) => msg.timestamp,
 104                 }
 105         }
 106 }
 107
 108 struct UtxoMessages {
 109         complete: Option<Result<TxOut, UtxoLookupError>>,
 110         channel_announce: Option<ChannelAnnouncement>,
 111         latest_node_announce_a: Option<NodeAnnouncement>,
 112         latest_node_announce_b: Option<NodeAnnouncement>,
 113         latest_channel_update_a: Option<ChannelUpdate>,
 114         latest_channel_update_b: Option<ChannelUpdate>,
 115 }
 116
 117 /// Represents a future resolution of a [`UtxoLookup::get_utxo`] query resolving async.
 118 ///
 119 /// See [`UtxoResult::Async`] and [`UtxoFuture::resolve`] for more info.
 120 #[derive(Clone)]
 121 pub struct UtxoFuture {
 122         state: Arc<Mutex<UtxoMessages>>,
 123 }
 124
 125 /// A trivial implementation of [`UtxoLookup`] which is used to call back into the network graph
 126 /// once we have a concrete resolution of a request.
 127 struct UtxoResolver(Result<TxOut, UtxoLookupError>);
 128 impl UtxoLookup for UtxoResolver {
 129         fn get_utxo(&self, _genesis_hash: &BlockHash, _short_channel_id: u64) -> UtxoResult {
 130                 UtxoResult::Sync(self.0.clone())
 131         }
 132 }
 133
 134 impl UtxoFuture {
 135         /// Builds a new future for later resolution.
 136         pub fn new() -> Self {
 137                 Self { state: Arc::new(Mutex::new(UtxoMessages {
 138                         complete: None,
 139                         channel_announce: None,
 140                         latest_node_announce_a: None,
 141                         latest_node_announce_b: None,
 142                         latest_channel_update_a: None,
 143                         latest_channel_update_b: None,
 144                 }))}
 145         }
 146
 147         /// Resolves this future against the given `graph` and with the given `result`.
 148         ///
 149         /// This is identical to calling [`UtxoFuture::resolve`] with a dummy `gossip`, disabling
 150         /// forwarding the validated gossip message onwards to peers.
 151         ///
 152         /// Because this may cause the [`NetworkGraph`]'s [`processing_queue_high`] to flip, in order
 153         /// to allow us to interact with peers again, you should call [`PeerManager::process_events`]
 154         /// after this.
 155         ///
 156         /// [`processing_queue_high`]: crate::ln::msgs::RoutingMessageHandler::processing_queue_high
 157         /// [`PeerManager::process_events`]: crate::ln::peer_handler::PeerManager::process_events
 158         pub fn resolve_without_forwarding<L: Deref>(&self,
 159                 graph: &NetworkGraph<L>, result: Result<TxOut, UtxoLookupError>)
 160         where L::Target: Logger {
 161                 self.do_resolve(graph, result);
 162         }
 163
 164         /// Resolves this future against the given `graph` and with the given `result`.
 165         ///
 166         /// The given `gossip` is used to broadcast any validated messages onwards to all peers which
 167         /// have available buffer space.
 168         ///
 169         /// Because this may cause the [`NetworkGraph`]'s [`processing_queue_high`] to flip, in order
 170         /// to allow us to interact with peers again, you should call [`PeerManager::process_events`]
 171         /// after this.
 172         ///
 173         /// [`processing_queue_high`]: crate::ln::msgs::RoutingMessageHandler::processing_queue_high
 174         /// [`PeerManager::process_events`]: crate::ln::peer_handler::PeerManager::process_events
 175         pub fn resolve<L: Deref, G: Deref<Target=NetworkGraph<L>>, U: Deref, GS: Deref<Target = P2PGossipSync<G, U, L>>>(&self,
 176                 graph: &NetworkGraph<L>, gossip: GS, result: Result<TxOut, UtxoLookupError>
 177         ) where L::Target: Logger, U::Target: UtxoLookup {
 178                 let mut res = self.do_resolve(graph, result);
 179                 for msg_opt in res.iter_mut() {
 180                         if let Some(msg) = msg_opt.take() {
 181                                 gossip.forward_gossip_msg(msg);
 182                         }
 183                 }
 184         }
 185
 186         fn do_resolve<L: Deref>(&self, graph: &NetworkGraph<L>, result: Result<TxOut, UtxoLookupError>)
 187         -> [Option<MessageSendEvent>; 5] where L::Target: Logger {
 188                 let (announcement, node_a, node_b, update_a, update_b) = {
 189                         let mut pending_checks = graph.pending_checks.internal.lock().unwrap();
 190                         let mut async_messages = self.state.lock().unwrap();
 191
 192                         if async_messages.channel_announce.is_none() {
 193                                 // We raced returning to `check_channel_announcement` which hasn't updated
 194                                 // `channel_announce` yet. That's okay, we can set the `complete` field which it will
 195                                 // check once it gets control again.
 196                                 async_messages.complete = Some(result);
 197                                 return [None, None, None, None, None];
 198                         }
 199
 200                         let announcement_msg = match async_messages.channel_announce.as_ref().unwrap() {
 201                                 ChannelAnnouncement::Full(signed_msg) => &signed_msg.contents,
 202                                 ChannelAnnouncement::Unsigned(msg) => &msg,
 203                         };
 204
 205                         pending_checks.lookup_completed(announcement_msg, &Arc::downgrade(&self.state));
 206
 207                         (async_messages.channel_announce.take().unwrap(),
 208                                 async_messages.latest_node_announce_a.take(),
 209                                 async_messages.latest_node_announce_b.take(),
 210                                 async_messages.latest_channel_update_a.take(),
 211                                 async_messages.latest_channel_update_b.take())
 212                 };
 213
 214                 let mut res = [None, None, None, None, None];
 215                 let mut res_idx = 0;
 216
 217                 // Now that we've updated our internal state, pass the pending messages back through the
 218                 // network graph with a different `UtxoLookup` which will resolve immediately.
 219                 // Note that we ignore errors as we don't disconnect peers anyway, so there's nothing to do
 220                 // with them.
 221                 let resolver = UtxoResolver(result);
 222                 match announcement {
 223                         ChannelAnnouncement::Full(signed_msg) => {
 224                                 if graph.update_channel_from_announcement(&signed_msg, &Some(&resolver)).is_ok() {
 225                                         res[res_idx] = Some(MessageSendEvent::BroadcastChannelAnnouncement {
 226                                                 msg: signed_msg, update_msg: None,
 227                                         });
 228                                         res_idx += 1;
 229                                 }
 230                         },
 231                         ChannelAnnouncement::Unsigned(msg) => {
 232                                 let _ = graph.update_channel_from_unsigned_announcement(&msg, &Some(&resolver));
 233                         },
 234                 }
 235
 236                 for announce in core::iter::once(node_a).chain(core::iter::once(node_b)) {
 237                         match announce {
 238                                 Some(NodeAnnouncement::Full(signed_msg)) => {
 239                                         if graph.update_node_from_announcement(&signed_msg).is_ok() {
 240                                                 res[res_idx] = Some(MessageSendEvent::BroadcastNodeAnnouncement {
 241                                                         msg: signed_msg,
 242                                                 });
 243                                                 res_idx += 1;
 244                                         }
 245                                 },
 246                                 Some(NodeAnnouncement::Unsigned(msg)) => {
 247                                         let _ = graph.update_node_from_unsigned_announcement(&msg);
 248                                 },
 249                                 None => {},
 250                         }
 251                 }
 252
 253                 for update in core::iter::once(update_a).chain(core::iter::once(update_b)) {
 254                         match update {
 255                                 Some(ChannelUpdate::Full(signed_msg)) => {
 256                                         if graph.update_channel(&signed_msg).is_ok() {
 257                                                 res[res_idx] = Some(MessageSendEvent::BroadcastChannelUpdate {
 258                                                         msg: signed_msg,
 259                                                 });
 260                                                 res_idx += 1;
 261                                         }
 262                                 },
 263                                 Some(ChannelUpdate::Unsigned(msg)) => {
 264                                         let _ = graph.update_channel_unsigned(&msg);
 265                                 },
 266                                 None => {},
 267                         }
 268                 }
 269
 270                 res
 271         }
 272 }
 273
 274 struct PendingChecksContext {
 275         channels: HashMap<u64, Weak<Mutex<UtxoMessages>>>,
 276         nodes: HashMap<NodeId, Vec<Weak<Mutex<UtxoMessages>>>>,
 277 }
 278
 279 impl PendingChecksContext {
 280         fn lookup_completed(&mut self,
 281                 msg: &msgs::UnsignedChannelAnnouncement, completed_state: &Weak<Mutex<UtxoMessages>>
 282         ) {
 283                 if let hash_map::Entry::Occupied(e) = self.channels.entry(msg.short_channel_id) {
 284                         if Weak::ptr_eq(e.get(), &completed_state) {
 285                                 e.remove();
 286                         }
 287                 }
 288
 289                 if let hash_map::Entry::Occupied(mut e) = self.nodes.entry(msg.node_id_1) {
 290                         e.get_mut().retain(|elem| !Weak::ptr_eq(&elem, &completed_state));
 291                         if e.get().is_empty() { e.remove(); }
 292                 }
 293                 if let hash_map::Entry::Occupied(mut e) = self.nodes.entry(msg.node_id_2) {
 294                         e.get_mut().retain(|elem| !Weak::ptr_eq(&elem, &completed_state));
 295                         if e.get().is_empty() { e.remove(); }
 296                 }
 297         }
 298 }
 299
 300 /// A set of messages which are pending UTXO lookups for processing.
 301 pub(super) struct PendingChecks {
 302         internal: Mutex<PendingChecksContext>,
 303 }
 304
 305 impl PendingChecks {
 306         pub(super) fn new() -> Self {
 307                 PendingChecks { internal: Mutex::new(PendingChecksContext {
 308                         channels: HashMap::new(), nodes: HashMap::new(),
 309                 }) }
 310         }
 311
 312         /// Checks if there is a pending `channel_update` UTXO validation for the given channel,
 313         /// and, if so, stores the channel message for handling later and returns an `Err`.
 314         pub(super) fn check_hold_pending_channel_update(
 315                 &self, msg: &msgs::UnsignedChannelUpdate, full_msg: Option<&msgs::ChannelUpdate>
 316         ) -> Result<(), LightningError> {
 317                 let mut pending_checks = self.internal.lock().unwrap();
 318                 if let hash_map::Entry::Occupied(e) = pending_checks.channels.entry(msg.short_channel_id) {
 319                         let is_from_a = (msg.flags & 1) == 1;
 320                         match Weak::upgrade(e.get()) {
 321                                 Some(msgs_ref) => {
 322                                         let mut messages = msgs_ref.lock().unwrap();
 323                                         let latest_update = if is_from_a {
 324                                                         &mut messages.latest_channel_update_a
 325                                                 } else {
 326                                                         &mut messages.latest_channel_update_b
 327                                                 };
 328                                         if latest_update.is_none() || latest_update.as_ref().unwrap().timestamp() < msg.timestamp {
 329                                                 // If the messages we got has a higher timestamp, just blindly assume the
 330                                                 // signatures on the new message are correct and drop the old message. This
 331                                                 // may cause us to end up dropping valid `channel_update`s if a peer is
 332                                                 // malicious, but we should get the correct ones when the node updates them.
 333                                                 *latest_update = Some(
 334                                                         if let Some(msg) = full_msg { ChannelUpdate::Full(msg.clone()) }
 335                                                         else { ChannelUpdate::Unsigned(msg.clone()) });
 336                                         }
 337                                         return Err(LightningError {
 338                                                 err: "Awaiting channel_announcement validation to accept channel_update".to_owned(),
 339                                                 action: ErrorAction::IgnoreAndLog(Level::Gossip),
 340                                         });
 341                                 },
 342                                 None => { e.remove(); },
 343                         }
 344                 }
 345                 Ok(())
 346         }
 347
 348         /// Checks if there is a pending `node_announcement` UTXO validation for a channel with the
 349         /// given node and, if so, stores the channel message for handling later and returns an `Err`.
 350         pub(super) fn check_hold_pending_node_announcement(
 351                 &self, msg: &msgs::UnsignedNodeAnnouncement, full_msg: Option<&msgs::NodeAnnouncement>
 352         ) -> Result<(), LightningError> {
 353                 let mut pending_checks = self.internal.lock().unwrap();
 354                 if let hash_map::Entry::Occupied(mut e) = pending_checks.nodes.entry(msg.node_id) {
 355                         let mut found_at_least_one_chan = false;
 356                         e.get_mut().retain(|node_msgs| {
 357                                 match Weak::upgrade(&node_msgs) {
 358                                         Some(chan_mtx) => {
 359                                                 let mut chan_msgs = chan_mtx.lock().unwrap();
 360                                                 if let Some(chan_announce) = &chan_msgs.channel_announce {
 361                                                         let latest_announce =
 362                                                                 if *chan_announce.node_id_1() == msg.node_id {
 363                                                                         &mut chan_msgs.latest_node_announce_a
 364                                                                 } else {
 365                                                                         &mut chan_msgs.latest_node_announce_b
 366                                                                 };
 367                                                         if latest_announce.is_none() ||
 368                                                                 latest_announce.as_ref().unwrap().timestamp() < msg.timestamp
 369                                                         {
 370                                                                 // If the messages we got has a higher timestamp, just blindly
 371                                                                 // assume the signatures on the new message are correct and drop
 372                                                                 // the old message. This may cause us to end up dropping valid
 373                                                                 // `node_announcement`s if a peer is malicious, but we should get
 374                                                                 // the correct ones when the node updates them.
 375                                                                 *latest_announce = Some(
 376                                                                         if let Some(msg) = full_msg { NodeAnnouncement::Full(msg.clone()) }
 377                                                                         else { NodeAnnouncement::Unsigned(msg.clone()) });
 378                                                         }
 379                                                         found_at_least_one_chan = true;
 380                                                         true
 381                                                 } else {
 382                                                         debug_assert!(false, "channel_announce is set before struct is added to node map");
 383                                                         false
 384                                                 }
 385                                         },
 386                                         None => false,
 387                                 }
 388                         });
 389                         if e.get().is_empty() { e.remove(); }
 390                         if found_at_least_one_chan {
 391                                 return Err(LightningError {
 392                                         err: "Awaiting channel_announcement validation to accept node_announcement".to_owned(),
 393                                         action: ErrorAction::IgnoreAndLog(Level::Gossip),
 394                                 });
 395                         }
 396                 }
 397                 Ok(())
 398         }
 399
 400         fn check_replace_previous_entry(msg: &msgs::UnsignedChannelAnnouncement,
 401                 full_msg: Option<&msgs::ChannelAnnouncement>, replacement: Option<Weak<Mutex<UtxoMessages>>>,
 402                 pending_channels: &mut HashMap<u64, Weak<Mutex<UtxoMessages>>>
 403         ) -> Result<(), msgs::LightningError> {
 404                 match pending_channels.entry(msg.short_channel_id) {
 405                         hash_map::Entry::Occupied(mut e) => {
 406                                 // There's already a pending lookup for the given SCID. Check if the messages
 407                                 // are the same and, if so, return immediately (don't bother spawning another
 408                                 // lookup if we haven't gotten that far yet).
 409                                 match Weak::upgrade(&e.get()) {
 410                                         Some(pending_msgs) => {
 411                                                 let pending_matches = match &pending_msgs.lock().unwrap().channel_announce {
 412                                                         Some(ChannelAnnouncement::Full(pending_msg)) => Some(pending_msg) == full_msg,
 413                                                         Some(ChannelAnnouncement::Unsigned(pending_msg)) => pending_msg == msg,
 414                                                         None => {
 415                                                                 // This shouldn't actually be reachable. We set the
 416                                                                 // `channel_announce` field under the same lock as setting the
 417                                                                 // channel map entry. Still, we can just treat it as
 418                                                                 // non-matching and let the new request fly.
 419                                                                 debug_assert!(false);
 420                                                                 false
 421                                                         },
 422                                                 };
 423                                                 if pending_matches {
 424                                                         return Err(LightningError {
 425                                                                 err: "Channel announcement is already being checked".to_owned(),
 426                                                                 action: ErrorAction::IgnoreDuplicateGossip,
 427                                                         });
 428                                                 } else {
 429                                                         // The earlier lookup is a different message. If we have another
 430                                                         // request in-flight now replace the original.
 431                                                         // Note that in the replace case whether to replace is somewhat
 432                                                         // arbitrary - both results will be handled, we're just updating the
 433                                                         // value that will be compared to future lookups with the same SCID.
 434                                                         if let Some(item) = replacement {
 435                                                                 *e.get_mut() = item;
 436                                                         }
 437                                                 }
 438                                         },
 439                                         None => {
 440                                                 // The earlier lookup already resolved. We can't be sure its the same
 441                                                 // so just remove/replace it and move on.
 442                                                 if let Some(item) = replacement {
 443                                                         *e.get_mut() = item;
 444                                                 } else { e.remove(); }
 445                                         },
 446                                 }
 447                         },
 448                         hash_map::Entry::Vacant(v) => {
 449                                 if let Some(item) = replacement { v.insert(item); }
 450                         },
 451                 }
 452                 Ok(())
 453         }
 454
 455         pub(super) fn check_channel_announcement<U: Deref>(&self,
 456                 utxo_lookup: &Option<U>, msg: &msgs::UnsignedChannelAnnouncement,
 457                 full_msg: Option<&msgs::ChannelAnnouncement>
 458         ) -> Result<Option<u64>, msgs::LightningError> where U::Target: UtxoLookup {
 459                 let handle_result = |res| {
 460                         match res {
 461                                 Ok(TxOut { value, script_pubkey }) => {
 462                                         let expected_script =
 463                                                 make_funding_redeemscript_from_slices(msg.bitcoin_key_1.as_slice(), msg.bitcoin_key_2.as_slice()).to_v0_p2wsh();
 464                                         if script_pubkey != expected_script {
 465                                                 return Err(LightningError{
 466                                                         err: format!("Channel announcement key ({}) didn't match on-chain script ({})",
 467                                                                 expected_script.to_hex(), script_pubkey.to_hex()),
 468                                                         action: ErrorAction::IgnoreError
 469                                                 });
 470                                         }
 471                                         Ok(Some(value))
 472                                 },
 473                                 Err(UtxoLookupError::UnknownChain) => {
 474                                         Err(LightningError {
 475                                                 err: format!("Channel announced on an unknown chain ({})",
 476                                                         msg.chain_hash.encode().to_hex()),
 477                                                 action: ErrorAction::IgnoreError
 478                                         })
 479                                 },
 480                                 Err(UtxoLookupError::UnknownTx) => {
 481                                         Err(LightningError {
 482                                                 err: "Channel announced without corresponding UTXO entry".to_owned(),
 483                                                 action: ErrorAction::IgnoreError
 484                                         })
 485                                 },
 486                         }
 487                 };
 488
 489                 Self::check_replace_previous_entry(msg, full_msg, None,
 490                         &mut self.internal.lock().unwrap().channels)?;
 491
 492                 match utxo_lookup {
 493                         &None => {
 494                                 // Tentatively accept, potentially exposing us to DoS attacks
 495                                 Ok(None)
 496                         },
 497                         &Some(ref utxo_lookup) => {
 498                                 match utxo_lookup.get_utxo(&msg.chain_hash, msg.short_channel_id) {
 499                                         UtxoResult::Sync(res) => handle_result(res),
 500                                         UtxoResult::Async(future) => {
 501                                                 let mut pending_checks = self.internal.lock().unwrap();
 502                                                 let mut async_messages = future.state.lock().unwrap();
 503                                                 if let Some(res) = async_messages.complete.take() {
 504                                                         // In the unlikely event the future resolved before we managed to get it,
 505                                                         // handle the result in-line.
 506                                                         handle_result(res)
 507                                                 } else {
 508                                                         Self::check_replace_previous_entry(msg, full_msg,
 509                                                                 Some(Arc::downgrade(&future.state)), &mut pending_checks.channels)?;
 510                                                         async_messages.channel_announce = Some(
 511                                                                 if let Some(msg) = full_msg { ChannelAnnouncement::Full(msg.clone()) }
 512                                                                 else { ChannelAnnouncement::Unsigned(msg.clone()) });
 513                                                         pending_checks.nodes.entry(msg.node_id_1)
 514                                                                 .or_insert(Vec::new()).push(Arc::downgrade(&future.state));
 515                                                         pending_checks.nodes.entry(msg.node_id_2)
 516                                                                 .or_insert(Vec::new()).push(Arc::downgrade(&future.state));
 517                                                         Err(LightningError {
 518                                                                 err: "Channel being checked async".to_owned(),
 519                                                                 action: ErrorAction::IgnoreAndLog(Level::Gossip),
 520                                                         })
 521                                                 }
 522                                         },
 523                                 }
 524                         }
 525                 }
 526         }
 527
 528         /// The maximum number of pending gossip checks before [`Self::too_many_checks_pending`]
 529         /// returns `true`. Note that this isn't a strict upper-bound on the number of checks pending -
 530         /// each peer may, at a minimum, read one more socket buffer worth of `channel_announcement`s
 531         /// which we'll have to process. With a socket buffer of 4KB and a minimum
 532         /// `channel_announcement` size of, roughly, 429 bytes, this may leave us with `10*our peer
 533         /// count` messages to process beyond this limit. Because we'll probably have a few peers,
 534         /// there's no reason for this constant to be materially less than 30 or so, and 32 in-flight
 535         /// checks should be more than enough for decent parallelism.
 536         const MAX_PENDING_LOOKUPS: usize = 32;
 537
 538         /// Returns true if there are a large number of async checks pending and future
 539         /// `channel_announcement` messages should be delayed. Note that this is only a hint and
 540         /// messages already in-flight may still have to be handled for various reasons.
 541         pub(super) fn too_many_checks_pending(&self) -> bool {
 542                 let mut pending_checks = self.internal.lock().unwrap();
 543                 if pending_checks.channels.len() > Self::MAX_PENDING_LOOKUPS {
 544                         // If we have many channel checks pending, ensure we don't have any dangling checks
 545                         // (i.e. checks where the user told us they'd call back but drop'd the `AccessFuture`
 546                         // instead) before we commit to applying backpressure.
 547                         pending_checks.channels.retain(|_, chan| {
 548                                 Weak::upgrade(&chan).is_some()
 549                         });
 550                         pending_checks.nodes.retain(|_, channels| {
 551                                 channels.retain(|chan| Weak::upgrade(&chan).is_some());
 552                                 !channels.is_empty()
 553                         });
 554                         pending_checks.channels.len() > Self::MAX_PENDING_LOOKUPS
 555                 } else {
 556                         false
 557                 }
 558         }
 559 }